NCAR Research Turns Commerical Aircraft into Turbulence Sensors

October 15, 1997
BOULDER--Since mid-September, researchers at the National Center for
Atmospheric Research (NCAR) in Boulder, Colorado, have been turning
commercial aircraft into in-flight "sensing platforms" to measure and
report turbulence. With funding from the Federal Aviation
Administration (FAA), NCAR scientist Larry Cornman and his colleagues
have created software that works with an aircraft's existing equipment
to measure and report in-situ (in-flight) turbulence once every minute.
United Airlines expects to deploy the software on more than 200
aircraft over the next six months. The data will be used to create
turbulence forecasts to help pilots steer clear of bumpy air. NCAR's
primary sponsor is the National Science Foundation.

Until now, the only data on turbulence--the sudden, invisible gusts
that buffet a plane and its passengers--came from pilot reports of
bouncy or choppy air. "If we'd tried to come up with a new sensor to
load onto the aircraft, it would have been too costly," explains
Cornman. Part of that cost comes from testing new equipment to ensure
that it does not affect flight operations. "So we looked for a way to
use sensors, computers, and communications systems that were already on
board, without interfering with their normal functions." Instead of
measuring turbulence directly, the researchers use the aircraft's
response to turbulence to deduce its magnitude.

"We're solving an inverse problem," says Cornman. "If I measure what
the aircraft's doing, I can infer what the turbulence must have been."
The result is an in-situ turbulence algorithm, or mathematical
problem-solving procedure, that uses measurements of how much the
aircraft is bouncing up and down while accounting for its weight, air
speed, altitude, and whether the plane is on autopilot or not.

The algorithm is incorporated into software installed by Allied Signal,
Inc., within Allied's onboard flight management system and aircraft
condition monitoring system. The data are then transmitted to an
FAA/National Weather Service (NWS) data base.

On average, a significant turbulence incident happens every other day
on a commercial flight somewhere in the United States. The result can
be everything from spilled food trays to broken bones for flight
attendants and passengers not buckled into their seats. In 1991, severe
turbulence tore the engine off a 747 cargo plane departing the
Anchorage airport. While a cause for the crash of United Flight 535 on
final approach to Colorado Springs airport in 1991 has never been
determined, turbulent winds and a rudder problem are thought to be the
most likely explanations.

Cornman and other scientists will use the data compiled on the FAA/NWS
data base to create a turbulence detection product--a view of flight
tracks showing what all of the aircraft in a given region have measured
in a 30-minute period. That flight track information will be provided
to United Airlines (and to other airlines as they become participants
in the future), as well as to the NWS Aviation Weather Center in Kansas
City, Missouri.

As more aircraft report more data, Cornman expects forecasting products
to improve to the point that "nowcasting," or turbulence warnings in
real time, will be possible. "Having such a comprehensive and accurate
data base will really boost our development of new forecasting tools,"
Cornman explains.

The International Civil Aviation Organization (ICAO) will compare
results from the U.S. in-situ turbulence detection program to ongoing
research at the Australian Bureau of Meteorology. ICAO's goal is an
international standard for turbulence measuring and reporting.

NCAR is managed by the University Corporation for Atmospheric
Research.

The National Center for Atmospheric Research and UCAR Office of Programs are operated by UCAR under the sponsorship of the National Science Foundation and other agencies. Opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any of UCARs sponsors. UCAR is an Equal Opportunity/Affirmative Action employer.